Paper 2 Flashcards
What is the functional group of alcohols?
-OH
What is the general formula of alcohols?
CnH2n+1OH
What are the properties of alcohols?
Flammable - can undergo complete combustion
Soluble - solution will have a neutral PH
Oxidised to form Carboxylic acid with (potassium dichromate (VI) and heat)
What happens when we oxidise an alcohol?
A carboxylic acid is formed
Potassium Dichromate (VI) is required and heat
What is the colour change of oxidation of alcohol using potassium dichromate (VI)
Potassium Dichromate (VI) turns from orange to green
What are the 3 ways alcohol can be oxidised?
Using an oxidising agent (potassium dichromate VI) in dilute sulfuric acid
Microbial oxidation - Carboxylic acid is produced as a by product as they use alcohol as their energy source
Combustion
What are the uses of alcohols?
Used as fuel
As solvents in industry
State two ways to produce ethanol?
Conditions
Ethen + steam: - Addition reaction
Phosphoric acid catalysts
300 degrees
60-70 atm pressure
Fermentation of glucose by yeast: - Anaerobic respiration
Requires yeast
30-40 degrees
Anaerobic conditions
Chemical equation for production of ethanol through hydration?
C2H4 + H20 -> C2H5OH
Chemical equation for production of ethanol through fermnetation?
C6H12O6 -> C2H5OH + CO2
Advantages and disadvantages of production of ethanol through hydration?
Pros:
No waste products - efficient
Cheap process
Cons:
Ethene is made from crude oil which is a finite resource
Advantages and disadvantages of production of ethanol through fermentation?
Pros:
Glucose is a renewable resource
Yeast are easy to grow
Cons:
Process is relatively slow
Ethanol is weak and not pure so has to be distilled and purified
Functional group of Carboxylic acid?
-COOH
Are carboxylic acids strong or weak acids?
What does that mean?
Weak acids - they don’t fully ionise.
All the carboxylic acids don’t all release their hydrogen ions
What happens when carboxylic acids react with metal carbonates?
Salt (magnesium ethanoate) + Water + Carbon Dioxide
What happens when carboxylic acids react with metals?
Salt + Hydrogen
How are carboxylic acids made?
By oxidising an alcohol
What are carboxylic acids used for?
Ethanoic acid is dissolved in water to make vinegar:
This is used for flavourings and preserving foods
What is the functional group of an ester?
Where is it found?
-COO- functional group found in the middle of the molecule
Alcohol + Carboxylic acid (with an acid catalyst) ->
Ester + water
How do we name an ester?
Alcohol forms the first part and acid forms the second part
eg. Methyl Propanoate
Characteristics of esters?
Pleasant smells (Sweet or fruity)
Volatile (Evaporate easily)
How do we make an ester? Method
Use ethyl ethanoate?
Ethanoic acid + Ethanol
- Add a few drops of concentrated sulfuric acid to a boiling tube using a dropping pipette
- Add 10 drops of ethanoic acid
- Add an equal volume of ethanol
- Place boiling tube, in a beaker of water, on a tripod.
- Heat till the water boils and then allow to cool
- Once it’s cool pour the mixture into a test tube of sodium carbonate solution and mix
- Layer of ester should form on the top (sweet smell)
Why does water form when an alcohol and carboxylic acid react?
As the carboxylic acid loses the -OH from its -COOH functional group
And the alcohol lose the H from its -OH functional group
These combine to form H2O
How are polyesters formed?
Using a diol and dicarboxylic acid
What does the dicarboxylic acid lose and diol lose to form a polyester?
Dicarboxylic acid loses - OH
Diol loses - H
How do you name polyesters?
Ester in brackets and add poly to the outside.
eg. Poly(Ethyl ethanoate)
How are some polyesters disposed of?
There are some polyesters that can biodegrade - these are called biopolyesters.
Bacteria and microorganisms can break down the ester links
They don’t stay in landfill forever and this therefore reduces the pollutant effect.
What is a dimer?
Two monomers combined
What goes in the pipette and what goes in the burette during a titration?
Known concentration goes in the pipette and unknown in the burette
Steps of an acid - alkali titration when you’re trying to find the concentration of acid?
- Using a pipette add 25cm3 of alkali to a clean conical flask
- Add a few drops of phenolphthalein to the conical flask and place it on a white tile (easier to see colour change)
- Fill the burette with acid below eye level (don’t want to be looking into the acid if it spills) and note the starting volume at eye level.
- Slowly add the acid drop by drop, swirling the conical flask to mix.
- Stop adding the acid when there is a colour change - the acid has neutralised the alkali
- Note final acid in burette and calculate how much acid was added.
- Repeat titration until you get concordant results - they are within 0.1 of each other.
- Use the concordant results to calculate the mean volume of acid required to neutralise the alkali
Why do we swirl the conical flask when doing titration?
So the mixture is evenly distributed to ensure the colour change occurs as soon as the titration occurs as soon as the neutralisation takes place.
Colour of Litmus in acid and alkali
Acid - red
Alkali - Blue
Colour of phenolphthalein in acid an alkali
Acid - colourless
Alkaline - pink
Colour of methyl orange in acid an alkali
Acid - Red
Alkaline - yellow
How are most metal oxides seperated?
Reduction using carbon (acts as a reducing agent)
Cheapest and easiest method
Copper oxide + carbon -> Copper + Carbon Dioxide
Why cant we reduce everything with carbon?
As some metals are more reactive than carbon
Potassium
Sodium
Lithium
Calcium
Magnesium
Carbon
What is above an below carbon in the reactivity series?
Magnesium
Aluminium
Carbon
Zinc
What is metallic bonding?
The strong electrostatic force of attraction between the lattice of positive ions and the sea of delocalized electrons
Why is there a sea of delocalised electrons in metals?
As when the atoms are arranged in their lattice they give up their outer shell electrons and share them with each other
Why can ionic compounds only conduct electricity when molten or in solution?
As only then can the ions move through the structure and carry a charge
Why are metals good conductors of electricity and heat?
The delocalised electrons can carry thermal energy and electrical current throughout the structure
How are metals malleable?
Layers of ions in a metal can slide over each other
What does malleable mean?
Bent or hammered into shapes
What is an alloy made of?
2 or more different elements
Why are alloys harder than pure metal?
Different sized atoms distort the regular layers of metal atoms so they cannot slide over each other.
Which ions move where in electrolysis?
What happens to them?
Cations (positive) move to the cathode (negative) and are reduced
Anions (negative) move towards the anode (positive) and are oxidised
Why don’t the electrodes react during electrolysis?
They’re made of an inert material
What is an electrolyte?
An liquid or or solution that contains an ionic compound where ions are free to move
How do we set up an electrochemical cell for an aqueous solution?
Get two inter electrodes eg. graphite or platinum
Clean the surfaces of the electrodes using emery paper
Place both electrodes into a beaker with the electrolyte
Connect the electrodes to a power supply using crocodile clips and wires.
Rules for electrolysis at the cathode in aqueous solution?
Cathode = Metals
H+ ions and Metal Ions are attracted to the cathode
Hydrogen gas will be produced if the metal is more reactive than hydrogen.
If less reactive then that pure metal will be produced
Rules of electrolysis at the anode in aqueous solution?
Anode = non metals
OH- and Non metal ions are present
If an OH- ion and a halide ion is present then that halide will be produced
If halides are not present oxygen will be formed
Half equation when oxygen is produced?
4OH- -> O2 +2H2O + 4e-
Method for how to make a soluble salt from an insoluble base and an acid?
Acid - Sulfuric Acid
Base - Copper (II) Oxide
- Heat acid in a water bath (in a fume cupboard) - speeds up reaction
- Then add the base in excess to the acid - until base no longer dissolves
- Filter off excess base - solution remaining is salt + water
- Heat the solution gently to evaporate off some water
- Stop heating when crystals begin to form on glass rod
- Leave for 24 hours to crystallise.
- Filter of solid crystals and leave to dry - left with copper sulfate crystals
How can we produce a dry sample of insoluble salt?
Not method
Mix two soluble salts - Precipitation reaction
eg. producing insoluble lead sulfate
Method for making dry lead (II) Sulfate?
Reactants: Lead Nitrate + Magnesium Sulfate
- Add one spatula of lead to a test tube. Dissolve in deionised water to ensure there are no other ions. Shake.
- Do the same with magnesium sulfate
- Tip the two solutions into a beaker and stir
- Lead sulfate will precipitate out
- Filter off the lead sulfate using filter paper
- Squirt deionised water into the beaker and filter again to ensure there is no lead sulfate left in the beaker
- Rinse filter paper with deionised water to ensure no magnesium sulfate is present.
- Scrape lead sulfate onto fresh filter paper and dry in oven or desiccator
How can we make a soluble salt using an acid/alkali reaction? Method
Using Titration:
Measure out a set amount of acid into a conical flask using a pipette.
Add a few drops of indicator
Slowly add alkali drop by drop from the burette into the conical flask, whilst swirling.
Do this until there is a colour change - acid neutralised
Record volume of alkali added
Now repeat without the indicator and add the recorded volume of alkali - no indicator so no contamination
Remaining solution is salt + water
Slowly evaporate off some of the water and then allow the solution to crystalise.
Filter off the solid and dry it - pure dry salt
Volume of gas = ?
Moles of gas x 24
Volume must be dm^3
What is Avogadro’s law?
One mole of any gas always occupies 24dm^3 at room temperature and pressure
Concentration in g/dm^3 = ?
mass / volume
Concentration is measure in?
Grams per dm^3
g/dm^3
Or
Moles per dm^3
moles/dm^3
Concentration in mol/dm^3 = ?
Moles / volume
How do you convert from moles per dm3 to grams per dm3
Multiply by the Mr of the solution
Axis of reaction profile?
Y axis is energy
X axis is progress of reaction
Describe a reaction profile for an exothermic reaction?
Products finish lower than reactants.
So enthalpy change is negative - the vertical distance between the reactants and the products
What is the activation energy?
The minimum amount of energy the reactants need to collide with each other and react.
Describe the reaction profile of an endothermic reaction.
Products finish higher than reactants as they take in energy from the surroundings.
Endothermic or exothermic: Bond breaking?
Endothermic as energy must be supplied.
Energy used to break the bonds is more than energy released forming them
Endothermic or exothermic: Bond forming?
Exothermic as energy is released when bonds are formed
Energy released forming the bonds is greater than the energy required breaking them
Enthalpy change = ? (bond energies)
Total energy absorbed breaking the bonds - total energy released forming the bonds
formula for enthalpy change?
kj/mol
What is dynamic equilibrium?
When a reversible reaction occurs in a closed system then a state of equilibrium will be reached where the rate of the forward reaction is equal to the rate of the backwards reaction.
The concentration of reactants and products will remain constant (given that there is no change to external conditions eg. Temperature or pressure)
Describe the thermal decomposition of ammonium chloride in terms of reversible reactions?
Ammonium Chloride is a white solid, when heated it breaks down into the gases ammonia and hydrogen chloride - forward reaction
When cooled it reforms the white solid ammonium chloride as the ammonia and hydrogen chloride react
How does temperature affect a reversible reaction?
Adding heat: Endothermic reaction will increase to use up the extra heat.
Removing heat: Exothermic reaction will speed up to give out more heat
How does pressure affect a reversible reaction?
Increasing pressure: Rate of reaction will increase on side which produces fewer moles of gas
Decreasing pressure: Rate of reaction will increase on the side which produces more moles of gas
Why does a catalyst not affect the position of equilibrium?
Speeds up the reaction in both the forwards and backwards directions by the same amount
Define solubility
The maximum amount of a substance the will dissolve in a given amount of solvent at a fixed temperature
Unit of solubility
g per 100g of solvent
What happens to solubility as temperature increases?
Solubility increases
Investigating solubility method - practical?
Put 50 cm3 of water into a beaker
Add salt to the water a little at a time until no more dissolves
Filter to obtain the saturated solution and remove the excess
Record the mass of an empty evaporating basin
Pour the saturated solution into the evaporating basin
Record the new mass
Gently heat the evaporating basin and solution to remove all the water
Record the mass of the evaporating basin an dry salt
Calculate mass of water and dry salt
Formula for solubility?
Mass of solid / mass of water removed x 100
What is the functional group?
Group of atoms in a compound that determines its chemical properties and reactions
